SYSTEM ANALYSIS THROUGH BOND GRAPH MODELING by ...

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modeled as a source and not a sink. Similarly, the SF element of figure 3.10 shows that
the flow information moves from left to right as defined by the causal mark, and the half
arrow depicts this element as a source as well.
Figure 3.10. Necessary Causality
Figure 3.11 shows the possible combinations for the causal assignments for the 2-port
elements. Also shown in figure 3.11 are the implied relationships between the conjugate
variables determined by each set of causal marks. The relationships between the
conjugate variables are defined by the causal mark, since the signal flow information
must remain consistent with the definition of the causal mark shown in figure 3.9. Note;
in figure 3.11, the conjugate variable equations for each case maintain the required
power-in equals power-out relationship.
The remaining 1-port elements have two possible combinations for causal mark
assignments. Each possibility implies specific relationships between the conjugate
variables. For the I and C elements there exists either an integral relationship or a
differential relationship between the conjugate variables. Figure 3.12 shows the integral
relationship with the proper causal mark for the I and C elements.